The system of recording an image by using silver halide grains as a photosensitive element and subjecting the image to so-called development processing to reproduce and preserve the image has developed remarkably in recent years and is applied in various fields. In particular, the market of color photographs, which many people use for the purpose of recording and appreciating images, is expanding year by year, and today everyone can readily obtain color prints.
On the other hand, new image-forming systems to which the technique of silver halide photographic materials is applied are suggested. As one such system, a system in which digitized image information is used to write an image directly into a photographic material can be mentioned. By using such a system, the gradation or the tone of the image data can be converted, or processing, for example for setting the layout arbitrarily, becomes possible. By using a laser beam as the output of digitized image information, an image output with high precision can be realized. By the recent development of laser diodes, production of simple and stable laser output apparatuses has become possible and the advent of such a system is expected. However, in laser diodes that now can be supplied stably, the emitting wavelength region is restricted to from the red region to the infrared region, and therefore in order to write image information using them it is necessary to use photographic materials that have spectral sensitivity in the infrared region. For example, U.S. Pat. Nos. 4,619,892 or 4,956,702 discloses a technique that uses a silver halide color photographic material provided with sensitivity in the infrared region as a photographic material for outputs from laser diodes.
In composing the above system, in the case wherein silver halide photographic materials are used, for example, the length of the processing time and the magnitude of the fluctuation of the processing are considered to constitute practical limitations. As a technique of overcoming these drawbacks, a method is known wherein color papers containing, instead of the silver chlorobromide emulsions conventionally widely used in photographic materials for color prints (hereinafter referred to as color papers), which are high in silver bromide content, so-called high-silver chloride emulsions, which are increased in silver chloride content, are processed. For example, International Application WO 87-04534 discloses a method of rapidly processing a color paper, wherein use is made of a high-silver chloride emulsion, with a color developer substantially free from sulfite ions and benzyl alcohol.
However, when spectral sensitivity was imparted to high-silver chloride emulsions to prepare photographic materials in which an image would be written by a laser diode and the photographic materials were subjected to various tests, it was found that the photographic materials had the following problems.
That is, even when high-silver chloride emulsions were sensitized to the infrared region, a high sensitivity was hardly available, and the fluctuation in sensitivity to such conditions as a change in temperature at the time of exposure was conspicuous. Further, it was made obvious that these drawbacks were inclined to be more aggravated in the case of high-intensity and short-period exposure, such as scanning exposure by a laser beam.
Many techniques for overcoming the above drawbacks involved in high-silver chloride emulsions have been reported to date.
For example, Japanese Patent Publication (OPI) Nos. Sho. 58-95736, 58-108533, 60-228844, and 60-222845 disclose high-silver chloride emulsions having different grain structures, with a layer having a high silver bromide content in silver halide grains, so as to impart a high sensitivity while suppressing fogging of the high-silver halide emulsions. However, the present inventors studied these techniques and as a result found that, according to these techniques, highly sensitive emulsions could indeed be obtained, but at the same time, when pressure was exerted on the emulsion grains, desensitization was liable to occur, constituting a major defect in practice.
On the other hand, Japanese Patent Application (OPI) No. Sho. 51-139323 or No. Sho. 59-171947 or British Patent Specification No. 2109576A, describes that when a compound of a metal of group VIII is incorporated, a high sensitivity is secured and reciprocity law failure is improved. Further, Japanese Patent Publication No. Sho. 49-33781, Japanese Patent Application (OPI) No. Sho. 50-23618, 52-18310, 58-15952, 59-214028, and 61-67845, German Patent Nos. 2,226,877 and 2,708,466, and U.S. Patent Specification No. 3,703,584 describe that when a rhodium compound or an iridium compound is incorporated, an improvement in high contrast and reciprocity law failure can be accomplished. However, when a rhodium compound is used, although a high-contrast emulsion can be obtained, conspicuous desensitization occurs, which is not preferable in practice. When an iridium compound is used, so-called latent-image sensitization, i.e., an increase in development density due to the lapse of time from the exposure of the photographic material to the processing, is observed strikingly, which is not preferable in practice.
Further, U.S. Pat. No. 4,269,927 describes that a high sensitivity can be obtained when cadmium, lead, copper, zinc, or a mixture of these is contained within surface-latent-image type high-silver chloride grains having a silver chloride content of 80 mol % or more. However, although these methods provide increase in sensitivity and a small effect of improving reciprocity law failure, the improvement in the fluctuation in sensitivity owing to a change in temperature at the time of exposure is not satisfactory.
Further, Japanese Patent Publication No. Sho. 48-35373 describes that a high-contrast black-and-white photographic print paper can be obtained inexpensively by mixing a water-soluble iron compound with a silver chloride emulsion obtained by the normal precipitation method. Although this method definitely increases the high intensity sensitivity of a silver chloride emulsion, the improvement in the fluctuation in sensitivity owing to a change in temperature at the time of exposure, particularly the improvement in temperature dependency of sensitivity of high-intensity exposure, is not satisfactory.
Further, Japanese Patent Application (OPI) No. Hei. 1-183647 describes that by placing a silver bromide localized layer in or on high-silver chloride grains containing iron ions, a high sensitivity can be obtained and the fluctuation in sensitivity owing to a change in temperature at the time of exposure can be alleviated. However, this method is not satisfactory enough to improve the temperature dependency of sensitivity of high-intensity exposure at the time of exposure.
Further, Japanese Patent Application (OPI) No. Hei. 3-84545 describes that a silver halide color photographic material, wherein each of three silver halide photosensitive layers that contain any one of a cyan coupler, a magenta coupler, and a yellow coupler, has spectral sensitivity peaks in three different wavelength regions of 650 nm or over; wherein the emulsions of these three photosensitive layers comprise silver chloride emulsions or silver chlorobromide emulsions containing 96 mol % or more of silver chloride; and wherein the emulsion of at least one of the three photosensitive layers comprises a silver iodochloride emulsion or a silver iodochlorobromide emulsion containing 0.01 to 3 mol % of silver iodide on the surface or sub-surface of the grains, said photographic material gives a high sensitivity and an effect less dependent on exposure temperature. But though such a photographic material does provide a remarkable effect, a further improvement in temperature dependency of high-intensity exposure sensitivity at the time of exposure is desired.